1. Field of the Invention
The present invention relates to a method of manufacturing a semiconductor device, and more particularly, it relates to a method of forming a polycide interconnection.
2. Description of the Prior Art
FIGS. 6 to 9 are cross-sectional views showing main steps of a conventional method of forming a polycide interconnection in a semiconductor device. The manufacturing process will be described below, referring to FIGS. 6 to 9.
Referring to FIG. 6, an interlayer insulating film 2 is formed on a semiconductor substrate 1. A polycrystal silicon film 3 is deposited on the interlayer insulating film 2 by a vacuum CVD technique. At this time, a natural oxide film 4 is formed sparsely on a surface of the polycrystal silicon film 3, as shown in the figure.
Then, the natural oxide film 4 is removed from the surface of the polycrystal silicon film 3 by performing RF etching (sputter etching) with a sputtering device.
After the sputter etching is completed, the sputtering device is employed again in another sputtering process. This time, a metal having a high fusing point such as tungsten silicide, for example, is deposited on the polycrystal silicon film 3, from which the natural oxide film 4 has been removed already, to form a metal silicide film 5, as shown in FIG. 8. Thus, the processings are continuously carried out under vacuum after the sputter etching.
Then, the polycrystal silicon film 3 and the metal silicide film 5 are patterned by performing a photolithography and etching process, thereby a polycide interconnection composed of the polycrystal silicon film 3 and the metal silicide film 5 is formed, as shown in FIG. 9. Further, an interlayer insulating film 6 is formed on the entire surface by a thermal oxidation technique.
A polycide interconnection has been conventionally formed in a semiconductor device as described above. According to the conventional method, it is always necessary to perform the sputter etching in order to remove the natural oxide film 4 which is formed on the surface of the polycrystal silicon film 3. During the sputter etching, a great quantity of particles are produced, which causes deterioration in product yield rate.
On the other hand, when the metal silicide film 5 is formed on the polycrystal silicon film 3 without performing the sputter etching to remove the natural oxide film 4 therefrom, particles are not produced. Therefore, deterioration in product yield rate can be controlled.
In this case, a problem arises when the interlayer insulating film 6 is formed on the metal silicide film 5 by a thermal oxidation technique which involves a heat treatment at a high temperature. When the natural oxide film 4 exists in the boundary face between the polycrystal silicon film 3 and the metal silicide film 5, silicon in the polyrystal silicon film 3 to be oxidixed is not uniformly supplied from the polycrystal silicon film 3 to the surface of the metal silicide film 5. As a result, cavities are produced in the boundary face, and the metal silicide film 5 is separated from the polycrystal silicon film 3 due to the cavities.